Lack of SARS-CoV-2-specific cellular response in critically ill COVID-19 patients despite apparent effective vaccination

© The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. The Creative Commons Public Domain Dedication waiver (http:// creat iveco mmons. org/ publi cdoma in/ zero/1. 0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Dear Editors, Since the beginning of the COVID-19 pandemic, messenger RNA vaccination has been highly effective for preventing SARS-CoV-2 infections [1]. However, hospitalizations in intensive care unit (ICU) have been reported among vaccinated patients characterized by advanced age or underlying comorbidities [2, 3]. Little is known about the specific cellular immune response of these patients upon ICU admission although this question is of utmost clinical importance. In a prospective cohort study, we assessed SARS-CoV2-specific immune response in 14 ICU patients (7 vaccinated and 7 non-vaccinated) between January and February 2022. Vaccinated patients received at least two doses of BNT162b2 vaccine with a delay ranging from two to six months. Of them, two had pre-existing immunosuppression (one kidney transplant and one mixed connective tissue disease). Demographic and clinical characteristics of the study population are provided in Additional file 1: Table S1. As controls, 8 vaccinated healthy volunteers (HV) were also enrolled. We evaluated humoral response by measuring antiSpike IgG titers. Cellular response was assessed by T-cell proliferation assay and whole blood Interferon-Gamma Release Assay (IGRA) after stimulation with SARS-Cov-2 proteins [4]. Upon ICU admission, vaccinated patients presented high anti-Spike IgG titers that were significantly higher than non-vaccinated patients (Fig. 1A). In contrast, T-cell proliferation in response to spike antigen was absent (Fig. 1B). In accordance, in response to SARS-CoV-2 antigens whole blood Interferon-Gamma Release Assay (IGRA) was found to be very low in vaccinated patients whereas they presented with strong response to mitogen (PHA) which illustrated appropriate functionality of T cell (Fig. 1C, D). As controls, HV showed good response in both lymphocyte proliferation and IGRA. Overall, these results indicate that despite apparent successful vaccination (i.e., illustrated by consistent seroconversion), patients admitted to ICU did not develop any cellular response to SARS-CoV-2. Of note, only 2 of 7 vaccinated patients, had previous history of immunosuppression. That said, as previously described in various ICU COVID-19 cohorts, present patients, vaccinated or not, presented with alterations in immune cellular parameters: profound lymphopenia and reduced monocytic HLA-DR expression (Fig. 1E, F). Although obtained in a relatively small cohort of patients, these results suggest that cellular response is also an important determinant of COVID-19 evolution in vaccinated patients. They raise concern about using humoral response as a sole metric of protective immunity following vaccination for SARS-CoV-2 especially in highrisk patients. Specific tools measuring cellular response, usable in a standardized routine practice, could guide the administration of COVID-19 vaccine booster in patients who did not mount any cellular response. This may help preventing evolution towards the most severe forms of Open Access

Dear Editors, Since the beginning of the COVID-19 pandemic, messenger RNA vaccination has been highly effective for preventing SARS-CoV-2 infections [1]. However, hospitalizations in intensive care unit (ICU) have been reported among vaccinated patients characterized by advanced age or underlying comorbidities [2,3]. Little is known about the specific cellular immune response of these patients upon ICU admission although this question is of utmost clinical importance.
In a prospective cohort study, we assessed SARS-CoV-2-specific immune response in 14 ICU patients (7 vaccinated and 7 non-vaccinated) between January and February 2022. Vaccinated patients received at least two doses of BNT162b2 vaccine with a delay ranging from two to six months. Of them, two had pre-existing immunosuppression (one kidney transplant and one mixed connective tissue disease). Demographic and clinical characteristics of the study population are provided in Additional file 1: Table S1. As controls, 8 vaccinated healthy volunteers (HV) were also enrolled.
We evaluated humoral response by measuring anti-Spike IgG titers. Cellular response was assessed by T-cell proliferation assay and whole blood Interferon-Gamma Release Assay (IGRA) after stimulation with SARS-Cov-2 proteins [4].
Upon ICU admission, vaccinated patients presented high anti-Spike IgG titers that were significantly higher than non-vaccinated patients (Fig. 1A). In contrast, T-cell proliferation in response to spike antigen was absent (Fig. 1B). In accordance, in response to SARS-CoV-2 antigens whole blood Interferon-Gamma Release Assay (IGRA) was found to be very low in vaccinated patients whereas they presented with strong response to mitogen (PHA) which illustrated appropriate functionality of T cell (Fig. 1C, D). As controls, HV showed good response in both lymphocyte proliferation and IGRA. Overall, these results indicate that despite apparent successful vaccination (i.e., illustrated by consistent seroconversion), patients admitted to ICU did not develop any cellular response to SARS-CoV-2. Of note, only 2 of 7 vaccinated patients, had previous history of immunosuppression. That said, as previously described in various ICU COVID-19 cohorts, present patients, vaccinated or not, presented with alterations in immune cellular parameters: profound lymphopenia and reduced monocytic HLA-DR expression (Fig. 1E, F).
Although obtained in a relatively small cohort of patients, these results suggest that cellular response is also an important determinant of COVID-19 evolution in vaccinated patients. They raise concern about using humoral response as a sole metric of protective immunity following vaccination for SARS-CoV-2 especially in highrisk patients. Specific tools measuring cellular response, usable in a standardized routine practice, could guide the administration of COVID-19 vaccine booster in patients who did not mount any cellular response. This may help preventing evolution towards the most severe forms of Open Access *Correspondence: fabienne.venet@chu-lyon.fr the disease. Considering that an uncoordinated T cell and antibody responses have been associated with disease progression [5], the understanding of mechanisms sustaining incomplete vaccination (presence of IgG but lack of T cell response) remains of utmost importance.
Additional file 1. Complementary methods and description of clinical data.

Author contributions
FBi, GM, ACL and FV were involved in the design, implementation, and day-today management of the study. FBi and ACL included participants in the study.

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Funding
RICO clinical study was supported by funds from the Hospices Civils de Lyon, Fondation HCL and Claude Bernard Lyon 1 University/Région Auvergne Rhône-Alpes. IGRA reagents were provided by bioMérieux. The funders had no role in study design, data collection and analysis, interpretation, decision to submit or writing of the manuscript.

Availability of data and materials
The datasets analyzed during the current study are available from the corresponding author on reasonable request.

Declarations Ethics approval and consent to participate
This project was part of an ongoing prospective observational clinical study (RICO, REA-IMMUNO-COVID). It was approved by ethics committee (Comité de Protection des Personnes Ile de France 1-N°IRB/IORG #: IORG0009918) under Agreement Number 2020-A01079-30. This clinical study was registered at ClinicalTrials.gov (NCT04392401). The committee waived the need for written informed consent because the study was observational, with a low risk to patients, and no specific procedure, other than routine blood sampling, was required. Oral information and non-opposition to inclusion in the study were mandatory and were systematically obtained before any blood sample was drawn. This was recorded in patients' clinical files. If a patient was unable to consent directly, non-opposition was obtained from the patient's legally authorized representative and reconfirmed from the patient at the earliest opportunity.

Consent for publication
Not applicable.

Competing interests
FBe is bioMérieux's employee. This private company had no role in the study design, result analysis and decision to publish this study. All other authors have declared no conflicts of interest.